Field of the Invention
The present invention relates to a process and an apparatus for manufacturing tyres.
More particularly, the invention is specifically directed to the process and equipment used for building green tyres, to be subsequently submitted to a vulcanisation cycle, thereby obtained the final product.
Description of Related Art
A tyre for vehicle wheels generally comprises a carcass structure including at least one carcass ply having respectively opposite end flaps in engagement with respective annular anchoring structures, integrated into the regions usually identified as “beads”, which have an inner diameter substantially corresponding to a so-called “fitting diameter” of the tyre on a respective mounting rim.
Associated with the carcass structure is a belt structure comprising one or more belt layers, located in radial superposed relationship with each other and with the carcass ply and having textile or metallic reinforcing cords with a crossed orientation and/or substantially parallel to the circumferential extension direction of the tyre. A tread band is applied to the belt structure at a radially external position, which tread band too is made of elastomeric material like other semifinished products constituting the tyre.
In addition, respective sidewalls of elastomeric material are applied to the side surfaces of the carcass structure, each extending from one of the side edges of the tread band until close to the respective annular anchoring structure to the beads. In tyres of the “tubeless” type, an air-tight coating layer, usually referred to as “liner” covers the inner surfaces of the tyre.
Subsequently to building of the green tyre carried out through assembly of the respective components, a moulding and vulcanisation treatment is generally carried out; it aims at causing structural stabilisation of the tyre through cross-linking of the elastomeric compositions and also at imprinting a desired tread pattern therein, as well as possible distinctive graphic marks at the tyre sidewalls.
The carcass structure and belt structure are generally made separately of each other in respective work stations, to be mutually assembled at a later time.
In more detail, manufacture of the carcass structure first contemplates application of the carcass ply or plies onto a building drum, to form a so-called “carcass sleeve” that is substantially cylindrical. The annular anchoring structures to the beads are fitted or formed on the opposite end flaps of the carcass ply or plies that are subsequently turned up around the annular structures themselves so as to enclose them in a loop.
Simultaneously, on a second or auxiliary drum a so-called “outer sleeve” is made which comprises the belt layers mutually applied in radially superposed relationship, and possibly the tread band applied at a radially external position to the belt layers. The outer sleeve is then picked up from the auxiliary drum to be coupled to the carcass sleeve. To this aim the outer sleeve is disposed coaxially around the carcass sleeve and afterwards the carcass ply or plies are shaped into a toroidal configuration by mutual axial approaching of the beads and simultaneous admission of fluid under pressure to the inside of the carcass sleeve, so as to determine radial expansion of the carcass plies until causing adhesion of same against the inner surface of the outer sleeve.
Assembling of the carcass sleeve to the outer sleeve can be carried out on the same drum as used for manufacture of the carcass sleeve, in which case reference is made to a “unistage building process”.
Also known are building processes of the so-called “two-stage” type in which a so-called “first-stage drum” is employed to make the carcass sleeve, while assembly between the carcass structure and outer sleeve is carried out on a so-called “second-stage drum” or “shaping drum” onto which the carcass sleeve picked up from the first-stage drum, and subsequently the outer sleeve picked up from the auxiliary drum are transferred.
U.S. Pat. No. 3,990,931 discloses a unistage building process in which a radially expandable drum is used to cause engagement of the carcass structure at the annular anchoring structures, and contractible in an axial direction to give rise to the conformation of the carcass ply following admission of fluid between the carcass ply and the drum itself. The building process therein described further shows that the fitting diameter internally defined by the annular anchoring structures of the tyre under processing is greater than the diameter of application of the carcass ply onto said drum.
U.S. Pat. No. 7,128,117 discloses a first-stage drum provided with a central portion and two end portions located at axially opposite positions relative to the central portion. The central portion is circumferentially divided into radially movable sectors to expand the central portion between a contracted position and a radially expanded position. The carcass sleeve formed on the first-stage drum has the annular reinforcing structures fitted on the drum end portions, carrying respective inflatable turning-up bags in axial abutment relationship against the central portion provided in the radially expanded condition for support of the carcass plies.
U.S. Pat. No. 6,390,166 discloses a first-stage drum in which the end portions are radially expandable and contractible together with the central portion, to enable engagement and removal of the carcass sleeve, and axially movable close to and away from each other to adapt the axial size of the drum to the width of the tyre being manufactured.
U.S. Pat. No. 3,826,297 contemplates use of a dismountable first-stage drum to enable disengagement of the carcass sleeve previously formed by positioning annular anchoring structures against side shoulders provided on the drum, and subsequently forming the carcass ply or plies through application of circumferentially consecutive strip-like elements to cover the circumferential extension of the first-stage drum.